The present invention relates to a touch responsive keying unit for an electronic keyboard musical instrument. In standard electronic key operated musical instruments the depression of individually selectable keys from the keyboard produce different tone signals. However, the volume of these tone signals is constant and independent of the depressive force applied to the key. In this type of instrument it is common to employ a separate, manually operative volume controller to collectively vary the level of the tone signals. This standard electric keyboard musical instrument fails to provide the instrument player with the same feel when the keys are depressed as is experienced in a non-electric kay instrument wherein the depression of a key mechanically causes a hammer to strike a string, and it furthermore fails to provide an output tone signal with varying peak amplitude.
Prior art touch responsive units have commonly attempted to overcome these disadvantages by the use of circuits which involved the controlled closing of manual switches to produce a voltage for controlling a keyer circuit. The control voltage produced depended upon the speed of contact closure. Other prior art devices produced a control signal by the depression of a key which moved a magnet past an associated coil. However, these and other prior art devices failed to simulate the correlation between the force applied to the key and the initial amplitude level of tone signal output and the subsequent variable slope of decay of the tone signal amplitude which is obtainable by mechanical damping in non-electric instruments. Furthermore, the assembly of the magnetic touch responsive devices was frequently difficult and expensive due to the necessity of providing close tolerance of the flux gaps in the magnetic circuit.